The present invention relates to a rack-and-pinion steering gear, in particular for controlling motor vehicles, and in particular to a rack-and-pinion steering gear having a central compression spring which is braced on a set screw provided in a housing and which urges the rack in the direction of a pinion via a thrust piece.
In conventional rack-and-pinion steering gears, it is usual for the rack with its teeth to be pressed constantly against the teeth of the pinion by a central compression spring and a thrust piece between them, and for the opposite side of the central compression spring to be braced on a set screw or on an element comparable to the set screw that assures a desired spacing in some other way than by means of a thread.
Between the plane contact sides of the thrust piece and set screw, an axial spacing must be provided that is at least equivalent to the thrust piece travel. The thrust piece travel is the change in spacing between the pinion and the rack as a consequence of their total toothing deviations, which are effective for spacing purposes during the actuation of the steering gear.
If a smaller thrust piece play is set with the set screw than would correspond to the thrust piece travel dictated by deviations, the steering gear can jam while being actuated.
On the other hand, in terms of the vehicle, as a rule only little thrust piece play is desired, so that bumps in the road will not cause irritating rattling noises in the rack-and-pinion steering gear.
When the steering force is introduced via the pinion, and also as a result of the restoring force from the vehicle chassis that acts on the rack and from bumps in the road while driving, the rack and thrust piece are pressed away from the pinion by the toothing engagement angle, until such time as the thrust piece contacts the set screw.
This kind of rack-and-pinion steering gear is known for instance from Published, Non-examined German Patent Application DE-OS 19 48 612. In it, the steering shaft, which is actuated from the steering wheel and is supported in a housing, has a steering pinion that engages a rack, which pinion is pressed against the rack by a bearing block indirectly by a compression spring by means of a slide supported in the housing. The bearing block rests with a cylindrical or spherical guide face on a corresponding bearing face on the slide. A compression spring that acts on the slide is braced in the housing on a set screw; to limit backward deflection of the slide and thus to assure an engagement between the rack and the steering pinion, the travel of the slide can be adjusted by a limiting ring.
The known rack-and-pinion steering gears, however, also have the disadvantage that deviations in planarity of the thrust piece and set screw can cause tilting of the thrust piece; that the thrust piece play that is actually present can be defined only with great difficult; and that bumps in the road can cause rattling noises even if the thrust piece play is only slight. Although these noises can be reduced by a stronger central compression spring, as a rule this makes the steering gear tighter.
The object of the invention is to overcome these disadvantages and to create a rack-and-pinion steering gear in which the undesired rattling noises are reliably avoided, which runs smoothly, and in which tilting of the thrust piece no longer occurs.
This object is attained with the invention as described hereafter. In particular, the invention includes a compensating disk between the thrust piece and the set screw which is disposed with a topside toward the thrust piece. The compensating disk has a ball zone that engages the inside of a ball socket that is disposed on and adapted to the underside of the thrust piece.
The invention accordingly essentially provides the disposition of two additional parts, namely first a compensating disk between the thrust piece and set screw, and second, an eccentric spring between the compensating disk and set screw, along with an altered shape of the thrust piece; on the side toward the thrust piece, the compensating disk preferably has a spherical form and rests in a ball socket, adapted to it, of the thrust piece. The shape of the ball socket can be designed to suit the requirements in terms of function and load.
The invention offers the advantage that because it is possible to rotate the compensating disk in the ball socket in both planes, the deviations in planarity can be compensated for, and that the desired thrust piece play can be defined simply and without ambiguity, or adjusted with the set screw.
The side of the compensating disk toward the set screw, or the plane surface of the set screw as well, has a portion equivalent at most to half the side face and is embodied as curve-like, that is, is curved. The eccentric spring is seated in a bore of the compensating disk, and the bore is located on the non-curved or in other words flat portion of the plane surface. The eccentric spring has the effect that if the spacing between the set screw and the thrust piece increases, the compensating disk tilts. As a result, regardless of the axial position of the thrust piece, a bridge always exists between the thrust piece and the set screw. Instead of the typically provided thrust piece play, an adjustable thrust piece spacing is accordingly employed.
It should be emphasized that the surface curvature and the disposition of the eccentric spring can also be provided on the set screw, instead of on the compensating disk.